Look for a pro-audio headphone amplifier. Behringer, for example, do good quality at price. They work for the professional market where cost effectivness and merit is key, so you could be sure that you dont pay only for the well designed box with cheap internals (as may be the issue at some audiophile market oriented small firms, which are good at producing nice boxes), but the price reflects quality. Whether you like or not the sound what comes out - is a different issue. But this is the black box issue of any audio gear.